Zhang Hongyang, Xu Luping, Yan Bo, Zhang Hua, Luo Liyan
School of Aerospace Science and Technology, Xidian University, Xi'an 710126, China.
School of Information and Communication, Guilin University of Electronic Technology, Guilin 541004, China.
Sensors (Basel). 2017 Jun 22;17(7):1468. doi: 10.3390/s17071468.
Maximum likelihood estimation (MLE) has been researched for some acquisition and tracking applications of global navigation satellite system (GNSS) receivers and shows high performance. However, all current methods are derived and operated based on the sampling data, which results in a large computation burden. This paper proposes a low-complexity MLE carrier tracking loop for weak GNSS signals which processes the coherent integration results instead of the sampling data. First, the cost function of the MLE of signal parameters such as signal amplitude, carrier phase, and Doppler frequency are used to derive a MLE discriminator function. The optimal value of the cost function is searched by an efficient Levenberg-Marquardt (LM) method iteratively. Its performance including Cramér-Rao bound (CRB), dynamic characteristics and computation burden are analyzed by numerical techniques. Second, an adaptive Kalman filter is designed for the MLE discriminator to obtain smooth estimates of carrier phase and frequency. The performance of the proposed loop, in terms of sensitivity, accuracy and bit error rate, is compared with conventional methods by Monte Carlo (MC) simulations both in pedestrian-level and vehicle-level dynamic circumstances. Finally, an optimal loop which combines the proposed method and conventional method is designed to achieve the optimal performance both in weak and strong signal circumstances.
最大似然估计（MLE）已在全球导航卫星系统（GNSS）接收机的一些捕获和跟踪应用中得到研究，并显示出高性能。然而，目前所有的方法都是基于采样数据推导和运行的，这导致了巨大的计算负担。本文提出了一种用于弱GNSS信号的低复杂度MLE载波跟踪环路，该环路处理相干积分结果而非采样数据。首先，利用信号幅度、载波相位和多普勒频率等信号参数的MLE代价函数来推导MLE鉴别函数。通过高效的列文伯格-马夸尔特（LM）方法迭代搜索代价函数的最优值。利用数值技术分析了其性能，包括克拉美-罗界（CRB）、动态特性和计算负担。其次，为MLE鉴别器设计了一种自适应卡尔曼滤波器，以获得载波相位和频率的平滑估计。通过蒙特卡罗（MC）仿真，在行人级和车辆级动态环境下，将所提环路在灵敏度、精度和误码率方面的性能与传统方法进行了比较。最后，设计了一种将所提方法与传统方法相结合的最优环路，以在弱信号和强信号环境下均实现最优性能。
